Gas analyte spectrum sharpening and separation with multi-dimensional micro-gc for gas chromatography analysis

ABSTRACT

The disclosure describes embodiments of an apparatus including a first gas chromatograph including a fluid inlet, a fluid outlet, and a first temperature control. A controller is coupled to the first temperature control and includes logic to apply a first temperature profile to the first temperature control to heat, cool, or both heat and cool the first gas chromatograph. Other embodiments are disclosed and claimed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation under 35 U.S.C. § 120 of U.S.application Ser. No. 15/925,322, filed 19 Mar. 2018 and still pending,which is a divisional of U.S. application Ser. No. 14/659,212, filed 16Mar. 2015 and now U.S. Pat. No. 9,921,192, which is a divisional of U.S.application Ser. No. 13/089,850, filed 19 Apr. 2011 and now U.S. Pat.No. 8,978,444, which in turn claims priority under 35 U.S.C. § 119(e) toU.S. Prov. App. No. 61/327,392, filed 23 Apr. 2010, whose entirecontents are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates generally to gas chromatography and inparticular, but not exclusively, to gas chromatography with gas analytespectrum sharpening and separation using individual, cascaded and/ormulti-dimensional micro gas chromatographs (micro-GCs).

BACKGROUND

Gas analysis can be an important means for detecting the presence andconcentration of certain chemicals in the gas and determining themeaning of the particular combination of chemicals present. In healthcare, for example, the presence of certain volatile organic compounds(VOCs) in exhaled human breath are correlated to certain diseases, suchas pneumonia, pulmonary tuberculosis (TB), asthma, lung cancer, liverdiseases, kidney diseases, etc. The correlations are especiallyevidential for lung-related diseases. In other applications, gasanalysis can be used to determine the presence of dangerous substancesincompatible with human presence, such as methane, carbon monoxide orcarbon dioxide in a mine.

Current gas analytical systems still rely heavily on large and expensivelaboratory instruments, such as gas chromatography (GC) and massspectrometry (MS). Most of these instruments (mass spectrometers inparticular) have operational characteristics that prevent significantreductions in their size, meaning that current gas analysis systems arelarge and expensive bench devices. In addition to being expensive andunwieldy, the large size of current gas analysis devices makeswidespread use of these instruments impossible.

GC column coatings are usually optimized for specific temperatures andchemicals, so that no single GC can separate a large array of chemicals,even by varying its temperature. Because existing GCs are large, heavyunits housed in labs, a carrier gas with many chemicals may need to besent to multiple locations for separation, which substantially increasescost. The gas analyte/volatile organic compound (VOC) concentrationdistribution (spectrum) usually is broadened when injected into the GCcolumn. In the application of portable gas analysis, there is no viablesolution to sharpen the analyte/VOC spectrum without loss of detectionlimit. Moreover, the current column focusing can only be achieved bydirect impinging liquid nitrogen or dry ice to a small section of bulkyGC column for focusing effect. Such approach is expensive and cannot beimplemented as a portable gas analysis system.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the present invention aredescribed with reference to the following Figs., wherein like referencenumerals refer to like parts throughout the various views unlessotherwise specified.

FIG. 1A is a side elevation drawing of an embodiment of a gas analysisdevice.

FIG. 1B is a plan view of the embodiment of a gas analysis device shownin FIG. 1.

FIG. 2A is a cross-sectional elevation drawing of an embodiment of aMEMS pre-concentrator that can be used in the embodiment of a gasanalysis device shown in FIGS. 1A-1B.

FIG. 2B is a cross-sectional elevation drawing of an alternativeembodiment of a MEMS pre-concentrator that can be used in the embodimentof a gas analysis device shown in FIGS. 1A-1B.

FIG. 3A is a plan view drawing of an embodiment of a MEMS gaschromatograph that can be used in the embodiment of a gas analysisdevice shown in FIGS. 1A-1B.

FIG. 3B is a cross-sectional elevation drawing of the embodiment of aMEMS gas chromatograph shown in FIG. 3A, taken substantially alongsection line I-I.

FIG. 3C is a cross-sectional elevation drawing of an alternativeembodiment of the MEMS gas chromatograph shown in FIG. 3B.

FIGS. 3D is a plan view of an alternative embodiment of a gaschromatograph that can be used in the embodiment of a gas analysisdevice shown in FIGS. 1A-1B.

FIG. 3E is a cross-sectional elevation drawing of the embodiment of agas chromatograph shown in FIG. 3D.

FIG. 4A is a plan view drawing of an embodiment of a detector array thatcan be used in the embodiment of a gas analysis device of FIGS. 1A-1B.

FIG. 4B is a cross-sectional elevation drawing of the embodiment of adetector array shown in FIG. 4A, taken substantially along section lineI-I.

FIG. 4C is a set of graphs illustrating an embodiment of unseparated orpartially separated chemicals and selective sensor responses to thepartially separated chemicals.

FIG. 5 is a schematic diagram of an alternative embodiment of a gasanalysis device and an embodiment of a system using the embodiment ofthe gas analysis device.

FIG. 6 is a schematic diagram of another alternative embodiment of a gasanalysis device and an embodiment of a system using the embodiment ofthe gas analysis device.

FIG. 7 is a plan-view schematic diagram of an additional alternativeembodiment of a gas analysis device.

FIG. 8 is a side elevation schematic diagram of an additionalalternative embodiment of a gas analysis device.

FIG. 9 is a side elevation schematic diagram of an additionalalternative embodiment of a gas analysis device.

FIG. 9A is a plan-view schematic of a further additional alternativeembodiment of a gas analysis device.

FIG. 9B is a plan-view schematic of a further additional alternativeembodiment of a gas analysis device.

FIG. 10 is a schematic of an embodiment of cascaded gas chromatographswith spectrum sharpening.

FIG. 11A is a graph of an embodiment of a detector response to anembodiment of a temperature profile applied to a gas chromatograph.

FIG. 11B is a graph of an embodiment of a detector response to analternative embodiment of a temperature profile applied to a gaschromatograph.

FIG. 11C is a graph of an embodiment of a temperature profile for a gaschromatograph.

FIG. 12A is a schematic of an embodiment of a gas chromatograph.

FIGS. 12B-12C are graphs of detector response to various embodiments oftemperature profiles applied to the embodiments of a gas chromatographsshown in FIG. 12A.

FIG. 13A is a schematic of an embodiment of a cascaded gaschromatograph.

FIGS. 13B-13C are graphs of embodiments of temperature profiles that canbe applied to the cascaded gas chromatograph of FIG. 13A.

FIGS. 14A-14B are schematics of an embodiment of a multi-dimensional gaschromatograph.

FIG. 15 is a schematic of an alternative embodiment of amulti-dimensional gas chromatograph.

FIG. 16 is a schematic of another alternative embodiment of amulti-dimensional gas chromatograph.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Embodiments of an apparatus, process and system for gas analysis inpoint-of-care medical applications are described herein. In thefollowing description, numerous specific details are described toprovide a thorough understanding of embodiments of the invention. Oneskilled in the relevant art will recognize, however, that the inventioncan be practiced without one or more of the specific details, or withother methods, components, materials, etc. In other instances,well-known structures, materials, or operations are not shown ordescribed in detail but are nonetheless encompassed within the scope ofthe invention.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, appearancesof the phrases “in one embodiment” or “in an embodiment” in thisspecification do not necessarily all refer to the same embodiment.Furthermore, the particular features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments.

FIGS. 1A and 1B together illustrate an embodiment of a small scale(e.g., handheld) gas analysis device 100. Device 100 includes asubstrate 102 on which are mounted a fluid handling assembly 101, acontroller 126 coupled to the individual elements within fluid handlingassembly 101, and a reading and analysis circuit 128 coupled to detectorarray 110 and to controller 126. The embodiment shown in the Figs.illustrates one possible arrangement of the elements on substrate 102,but in other embodiments the elements can, of course, be arranged on thesubstrate differently.

Substrate 102 can be any kind of substrate that provides the requiredphysical support and communication connections for the elements ofdevice 100. In one embodiment, substrate 102 can be a printed circuitboard (PCB) of the single-layer variety with conductive traces on itssurface, but in other embodiments it can be a PCB of the multi-layervariety with conductive traces in the interior of the circuit board. Inother embodiments, for example an embodiment where device 100 is builtas a monolithic system on a single die, substrate 102 can be chip orwafer made of silicon or some other semiconductor. In still otherembodiments, substrate 102 can also be a chip or wafer in which opticalwaveguides can be formed to support optical communication between thecomponents of device 100.

Fluid handling assembly 101 includes a filter and valve assembly 104, apre-concentrator 106, a gas chromatograph 108, a detector array 110 anda pump 112. Elements 104-112 are fluidly coupled in series: filter andvalve assembly 104 is fluidly coupled to pre-concentrator 106 by fluidconnection 116, pre-concentrator 106 is fluidly coupled to gaschromatograph 108 by fluid connection 118, gas chromatograph 108 isfluidly coupled to detector array 110 by fluid connection 120, anddetector array 110 is coupled to pump 112 by fluid connection 122. Asfurther described below, in one embodiment of device 100 elements104-112 can be micro-electro-mechanical (MEMS) elements or MEMS-basedelements, meaning that some parts of each device can be MEMS and otherparts not. In other embodiments of device 100, some or all of elements104-112 need not be MEMS or MEMS-based, but can instead be some non-MEMSchip scale device.

As indicated by the arrows in the Figs., the fluid connections betweenelements 104-112 allow a fluid (e.g., one or more gases) to enter filterand valve assembly 104 through inlet 114, flow though elements 104-112,and finally exit pump 112 through outlet 124. Fluid handling assembly101 also includes a shroud or cover 125 that protects individualelements 104-112. In the illustrated embodiment, channels formed inshroud 125 provide the fluid connections between the elements, but inother embodiments the fluid connections between elements can be providedby other means, such as tubing. In still other embodiments shroud 125can be omitted.

Filter and valve assembly 104 includes an inlet 114 and an outletcoupled to fluid connection 116 such that fluid exiting filter and valveassembly 104 flows into pre-concentrator 106. Filter and valve assembly104 includes a filter to remove particulates from fluid entering throughinlet 114. In embodiments of device 100 where one or more of elements104-112 is a MEMS element, the small scale of parts within the MEMSelements means that fluid entering through inlet 114 might need to befiltered to remove these particles so that the particles do not enterthe MEMS elements and either them or render them inoperative. Inembodiments of device 100 that include no MEMS components, or wherefluid entering inlet 114 contains no particles, for instance because ithas been pre-filtered externally to device 100, the filter portion offilter and valve assembly 104 can be omitted.

Filter and valve assembly 104 also includes a valve so that further flowthrough inlet 114 into fluid handling assembly 101 can be stopped oncesufficient fluid has passed through the device. Stopping further flowthrough inlet 114 prevents dilution of fluids that will flow out ofpre-concentrator 106 during later operation of device 100 (seedescription of operation below). In other embodiments, filter and valveassembly 104 can also include a dehumidifier to remove water vapor fromthe fluid entering through inlet 114, thus improving the accuracy andsensitivity of device 100.

Pre-concentrator 106 includes an inlet coupled to fluid connection 116and an outlet coupled to fluid connection 118. Pre-concentrator 106receives fluid from filter and valve assembly 104 through fluidconnection 116 and outputs fluid to gas chromatograph 108 through fluidconnection 118. As fluid flows through pre-concentrator 106, thepre-concentrator absorbs certain chemicals from the passing fluid, thusconcentrating those chemicals for later separation and detection. In oneembodiment of device 100 pre-concentrator 106 can be a MEMSpre-concentrator, but in other embodiments pre-concentrator 106 can be anon-MEMS chip scale device. Further details of an embodiment of a MEMSpre-concentrator are described below in connection with FIG. 2.

Gas chromatograph 108 includes an inlet coupled to fluid connection 118and an outlet coupled to fluid connection 120. Gas chromatograph 108receives fluid from pre-concentrator 106 through fluid connection 118and outputs fluid to detector array 110 through fluid connection 120. Asfluid received from pre-concentrator 106 flows through gas chromatograph108, individual chemicals in the fluid received from thepre-concentrator are separated from each other in the time domain forlater input into detector array 110. In one embodiment of device 100 gaschromatograph 108 can be a MEMS gas chromatograph, but in otherembodiments gas chromatograph 108 can be a non-MEMS chip scale device.Further details of an embodiment of a MEMS gas chromatograph 108 aredescribed below in connection with FIGS. 3A-3C. Although shown in thedrawing as a single chromatograph, in other embodiments gaschromatograph 108 can be any of the gas chromatographs shown in FIG. 10et seq. In an embodiment in which gas chromatograph 108 includesmultiple chromatographs, it can be necessary to adjust the number ofdownstream and/or upstream components in device 100 to coincide with theinput or output configuration of the gas chromatograph. For instance, ifthe chromatograph 1400 shown in FIG. 14A is used as chromatograph 108 indevice 100, it can be necessary to adjust the number of detector arrays110, pumps 112, and so forth, to correspond to the number of outputs ofchromatograph 1400.

Detector array 110 includes an inlet coupled to fluid connection 120 andan outlet coupled fluid connection 122. Detector array 110 receivesfluid from gas chromatograph 108 through fluid connection 120 andoutputs fluid to pump 112 through fluid connection 122. As fluid flowsthrough detector array 110, the chemicals that were time-domainseparated by gas chromatograph 108 enter the detector array and theirpresence and/or concentration is sensed by sensors within the detectorarray. In one embodiment of device 100 detector array 110 can be a MEMSdetector array, but in other embodiments detector array 110 can be anon-MEMS chip scale device. Further details of an embodiment of adetector array 110 are described below in connection with FIG. 4.Although shown in the Fig. as a single detector array, in otherembodiments detector array 110 can actually include multiple detectorarrays. For example, in an embodiment where gas chromatograph 108 is aconfiguration made up of several individual chromatographs, such aschromatograph 1400 shown in FIG. 14, it can be necessary to adjust thenumber of detector arrays to match the output configuration of thecascaded chromatographs.

Pump 112 includes an inlet coupled to fluid connection 122, as well asan outlet coupled to an exhaust 124, such that pump 112 draws fluid fromdetector array 110 through fluid connections 122 and returns it to theatmosphere through exhaust 124. Pump 112 can be any kind of pump thatmeets the size and form factor requirements of device 100, provides thedesired flow rate and flow rate control, and has adequate reliability(i.e., adequate mean time between failures (MTBF)). In one embodiment,pump 112 can be a MEMS or MEMS-based pump, but in other embodiments itcan be another type of pump. Examples of pumps that can be used includesmall axial pumps (e.g., fans), piston pumps, and electro-osmotic pumps.Although shown in the Fig. as a single pump, in other embodiments pump112 can actually be made up of multiple pumps. For example, in anembodiment where gas chromatograph 108 is a cascaded configuration madeup of several individual chromatographs, such as chromatograph 1400shown in FIG. 14, it can be necessary to adjust the number of pumps tomatch the output configuration of the cascaded chromatographs.

Controller 126 is communicatively coupled to the individual elementswithin fluid handling assembly 101 such that it can send control signalsand/or receive feedback signals from the individual elements. In oneembodiment, controller 126 can be an application-specific integratedcircuit (ASIC) designed specifically for the task, for example a CMOScontroller including processing, volatile and/or non-volatile storage,memory and communication circuits, as well as associated logic tocontrol the various circuits and communicate externally to the elementsof fluid handling assembly 101. In other embodiments, however,controller 126 can instead be a general-purpose microprocessor in whichthe control functions are implemented in software. In the illustratedembodiment controller 126 is electrically coupled to the individualelements within fluid handling assembly 101 by conductive traces 130 onthe surface or in the interior of substrate 102, but in otherembodiments controller 126 can be coupled to the elements by othermeans, such as optical.

Readout and analysis circuit 128 is coupled to an output of detectorarray 110 such that it can receive data signals from individual sensorswithin detector array 110 and process and analyze these data signals. Inone embodiment, readout and analysis circuit 128 can be anapplication-specific integrated circuit (ASIC) designed specifically forthe task, such as a CMOS controller including processing, volatileand/or non-volatile storage, memory and communication circuits, as wellas associated logic to control the various circuits and communicateexternally. In other embodiments, however, readout and analysis circuit128 can instead be a general-purpose microprocessor in which the controlfunctions are implemented in software. In some embodiments readout andanalysis circuit 128 can also include signal conditioning and processingelements such as amplifiers, filters, analog-to-digital converters,etc., for both pre-processing of data signals received from detectorarray 110 and post-processing of data generated or extracted from thereceived data by readout and analysis circuit 128.

In the illustrated embodiment, readout and analysis circuit 128 iselectrically coupled to detector array 110 by conductive traces 132positioned on the surface or in the interior of substrate 102, but inother embodiments controller 126 can be coupled to the elements by othermeans, such as optical means. Readout and analysis circuit 128 is alsocoupled to controller 126 and can send signals to, and receive signalsfrom, controller 126 so that the two elements can coordinate andoptimize operation of device 100. Although the illustrated embodimentshows controller 126 and readout and analysis circuit 128 as physicallyseparate units, in other embodiments the controller and the readout andanalysis circuit could be combined in a single unit.

In operation of device 100, the system is first powered up and anynecessary logic (i.e., software instructions) is loaded into controller126 and readout and analysis circuit 128 and initialized. Afterinitialization, the valve in filter and valve unit 104 is opened andpump 112 is set to allow flow through the fluid handling assembly. Fluidis then input to fluid handling assembly 101 through inlet 114 at acertain flow rate and/or for a certain amount of time; the amount oftime needed will usually be determined by the time needed forpre-concentrator 106 to generate adequate concentrations of theparticular analytes (e.g., chemicals or VOCs) whose presence and/orconcentration are being determined. As fluid is input to the systemthrough inlet 114, it is filtered by filter and valve assembly 104 andflows through elements 104-112 within fluid handling assembly 101 byvirtue of the fluid connections between these elements. After flowingthrough elements 104-112, the fluid exits the fluid handling assemblythrough exhaust 124.

After the needed amount of fluid has been input through inlet 114, thevalve in filter and valve assembly 104 is closed to prevent furtherinput of fluid. After the valve is closed, a heater in pre-concentrator106 activates to heat the pre-concentrator. The heat releases thechemicals absorbed and concentrated by the pre-concentrator. As thechemicals are released from pre-concentrator 106, pump 112 is activatedto draw the released chemicals through gas chromatograph 108 anddetector array 110 and output the chemicals through exhaust 124.Activation of pump 112 also prevents backflow through fluid handlingassembly 101.

As the chemicals released from pre-concentrator 106 are drawn by pump112 through gas chromatograph 108, the chromatograph separates differentchemicals from each other in the time domain—that is, differentchemicals are output from the gas chromatograph at different times. Asthe different chemicals exit gas chromatograph 108 separated in time,each chemical enters MEMS detection array 110, where sensors in thedetection array detect the presence and/or concentration of eachchemical. The time-domain separation performed in gas chromatograph 108substantially enhances the accuracy and sensitivity of MEMS detectionarray 110, since it prevents numerous chemicals from entering thedetection array at the same time and thus prevents cross-contaminationand potential interference in the sensors within the array.

As individual sensors within MEMS detection array 110 interact with theentering time-domain-separated chemicals, the detection array senses theinteraction and outputs a signal to readout and analysis circuit 128,which can then use the signal to determine presence and/or concentrationof the chemicals. When readout and analysis circuit 128 has determinedthe presence and/or concentration of all the chemicals of interest itcan use various analysis techniques, such as correlation and patternmatching, to extract some meaning from the particular combination ofchemicals present and their concentrations.

FIG. 2A illustrates an embodiment of a MEMS pre-concentrator 200 thatcan be used as pre-concentrator 106 in device 100. Pre-concentrator 200includes a substrate 202 having a cover plate 204 bonded thereto andsealed around the perimeter of the substrate to create a cavity 206.Substrate 202 has formed therein an inlet 208 on one side, an outlet 210on a different side, and pockets 212 a-212 g having absorbents therein.In one embodiment, substrate 202 is a silicon substrate, but in otherembodiments substrate 202 can of course be made of other materials.Heater 216 is formed on the side of substrate 202 opposite the sidewhere cover plate 204 is attached.

In an embodiment where substrate 202 is silicon, inlet 208, outlet 210and pockets 212 a-212 g can be formed using standard photolithographicpatterning and etching. Although the illustrated embodiment shows sevenpockets 212 a-212 g, the number of pockets needed depends on the numberof different chemicals to be absorbed and concentrated, and on thenature of the absorbents used. In an embodiment where each absorbentabsorbs only one chemical, the number of pockets 212 a-212 g cancorrespond exactly to the number of chemicals to be absorbed andconcentrated, but in other embodiments where each absorbent absorbs onlyone chemical a greater number of pockets can be used to increase theabsorption area. In still other embodiments where each absorbent canabsorb more than one chemical, a lesser number of pockets can be used.

Each pocket 212 has a corresponding absorbent 214 in its interior—pocket212 a has absorbent 214 a, pocket 212 b has absorbent 214 b, and so on.Although shown in the illustrated embodiment as a granular absorbent, inother embodiments absorbents 214 can be coatings on the walls of pockets212 or can be a continuous substance that partially or fully fills eachpocket 212. Other embodiments can include combinations of granular, wallcoatings or continuous filling absorbents. Each absorbent can have achemical affinity for one or more particular chemicals, meaning that theexact absorbents used will depend on the number and nature of chemicalsto be absorbed and concentrated. Examples of absorbents that can be usedinclude Carbopack B, Carbopack X, etc.

During operation of MEMS pre-concentrator 200 in device 100, fluid fromfilter and valve assembly 104 enters through inlet 208, passes throughabsorbent 214 a in pocket 212 a, and enters cavity 206. Cover plate 204helps guide fluid entering the cavity 206 into the different pockets 212b-212 g and through absorbents 214 b-214 g, until the fluid, minus thechemicals absorbed by absorbents 214 a-214 g, exits the pre-concentratorthrough outlet 210. Once enough fluid has flowed through thepre-concentrator, the valve in filter and valve assembly 104 is closedto prevent further flow through inlet 208. Heater 216 is then activated.Heater 216 heats absorbents 214 a-214 f, causing them to release theabsorbed chemicals through processes such as outgassing. Simultaneouslywith activating heater 216, or shortly thereafter, pump 112 isactivated, drawing the released chemicals out through outlet 210 to gaschromatograph 108.

FIG. 2B illustrates an alternative embodiment of a MEMS pre-concentrator250. MEMS pre-concentrator 250 is in many respects similar to MEMSpre-concentrator 200. The primary difference between the two is that inMEMS pre-concentrator 250, the cover plate 252 is directly bonded to thesubstrate 202 without formation of cavity 206 found in cover plate 252.In one embodiment of MEMS pre-concentrator 250, channels/openings 254can exist in substrate 202 between the different pockets 212 a-212 g toallow the fluid to flow through adjacent pockets. In operation of MEMSpre-concentrator 250, fluid enters through inlet 208, passes through thedifferent pockets 212 a-212 g via the channels/openings 254 between thepockets, and finally exits the pre-concentrator through outlet 210.

FIGS. 3A-3B illustrate embodiments of an individual MEMS gaschromatograph 300 that can be used as GC 108 in device 100. MEMS gaschromatograph 300 includes a substrate 302 with an inlet 306 on oneside, an outlet 308 on a different side, and a separation column 310having a stationary phase coating on its walls. A cover plate 304 isbonded to substrate 302 to seal column 310. In one embodiment substrate302 is a silicon substrate, but in other embodiments substrate 302 canof course be made of other materials. In an embodiment where substrate302 is silicon, inlet 306, outlet 308 and column 310 can be formed usingstandard photolithographic patterning and etching, such as deep reactiveion etching (DRIE). Temperature control 314 is formed on the side ofsubstrate 302 opposite the side where cover plate 204 is attached. Inone embodiment, temperature control is integrated with chromatograph 300and can include heating elements and/or cooling elements, or elementsthat are capable of both heating and cooling such as a Peltier device orthermo-electric cooler (TEC). In embodiments where GC 300 is small (˜1inch range in one embodiment), it can be heated and cooled quickly withthese devices. Temperature control 314 can also include one or moretemperature sensors 316 to allow for monitoring and/or feedback controlof temperature control 314.

Channel or column 310 provides a continuous fluid path from inlet 306 tooutlet 308, and some or all of the walls of column 310 are coated with astationary phase coating that can interact with the chemicals beingseparated by the chromatograph or, in other words, the column walls arecoated with specific materials that have specific selectivity/separationpower for the desired gas analysis. How thoroughly and how fastchemicals are separated from the fluid depend on the stationary phasecoating, the overall path length of column 310, and the temperature. Fora given stationary phase coating, the longer the column the better thechemical spectrum separation, but a long column also extends theseparation time. For a given application, the required path length willtherefore usually be determined by a tradeoff among the coating, thecolumn length and the temperature. The illustrated embodiment showscolumn 310 as a spiral column in which the column path length willdepend on the number of coils in the spiral. In other embodiments,however, column 310 can be shaped differently. In one embodiment, column310 can be between 1 m and 10 m in length, but in other embodiment canbe outside this range. In the illustrated MEMS GC, column 310 can beformed by micromachining or micro-electro-mechanical-systems (MEMS)process on silicon wafer, glass wafer, PCB board, or any type ofsubstrate.

During operation of MEMS gas chromatograph 300 in device 100, fluid frompre-concentrator 106 enters through inlet 306 and passes through column310. As fluid passes through the column 310, the different chemicals inthe fluid interact with stationary phase coating 312 at different rates,meaning that the chemicals are separated after traveling through thecolumn, with the chemicals that interact strongly with the stationaryphase being separated first and the chemicals that interact weakly withthe stationary phase being separated last. In other words, chemicalsthat interact strongly with the stationary phase are retained longer inthe stationary phase, while chemicals that interacted weakly with thestationary phase retained less time in the stationary phase. In someembodiments of gas chromatograph 300 this time-domain separation canoccur according to molecular weight (e.g., chemicals with the lowestmolecular weight are separated first, followed by higher molecularweights), but in other embodiments it can occur according to otherchemical characteristics or other separation mechanisms. As thechemicals are time-domain separated, pump 112 draws them out of MEMS gaschromatograph 300 through outlet 308. Generally, the chemicals exitthrough outlet 308 in the reverse order of their separation—that is,chemicals with low retention time exit first, while chemicals withhigher retention times exit later. After leaving outlet 308, thechemicals enter detector array 110.

FIG. 3C illustrates an alternative embodiment of an individual gaschromatograph 350. Gas chromatograph 350 is in most respects similar togas chromatograph 300 shown in FIG. 3B. The primary difference betweengas chromatographs 300 and 350 is the configuration of the temperaturecontrol. In gas chromatograph 350, temperature control 352 is notintegrated into the chromatograph, but instead is an external component,such as a Peltier device, a thermo-electric cooler (TEC) or a heatingand/or cooling plate, that is thermally coupled to the chromatograph.Thermal coupling between external temperature control 352 and thechromatograph can be accomplished, for example, using thermallyconductive adhesives or with thermal interface materials. As withtemperature control 314, temperature control 352 can include one or moretemperature sensors 354 to monitor the temperature and/or providefeedback control of the temperature control. Since the GC is small(about 1 inch range in one embodiment, but not limited to this range),fast heating and cooling control can be achieved with either theintegrated or external temperature controls.

FIGS. 3D and 3E together illustrate an alternative embodiment of anindividual gas chromatograph 380. The primary difference between gaschromatographs 380 and 350 is the formation in chromatograph 380 of aconventional chromatography column instead of a MEMS chromatographycolumn. Gas chromatograph 380 includes a substrate 382 having a cavityor opening 384 therein. Positioned within cavity 384 is a chromatographycolumn 386, which in one embodiment can be formed using coiled capillarytube used in conventional chromatography. In one embodiment the lengthof column 386 can be from 1-10 m, but in other embodiments it can benecessary to limit the length to 1-3 m because of the more bulkyconfiguration. A temperature control 390 is bonded to substrate 382 toclose cavity 384, thus enclosing column 386. In one embodiment,temperature control 390 can be an external temperature control as shownand described for FIG. 3C, and can include one or more temperaturesensors 388 to monitor the temperature and/or provide feedback controlof the temperature control. GC 380 can be packaged in a small size toachieve faster heating and cooling control.

Operation of gas chromatograph 380 is similar to gas chromatograph 350shown in FIG. 3C. The primary difference between gas chromatographs 380and 350 is the formation of chromatography column. Instead of using MEMSfabricated column chip, the column can be formed by coiled capillarytube used in conventional chromatography. The column is then enclosed bya temperature control 390 as shown in FIG. 3E. Such a GC can be packagedin a small size to achieve faster heating and cooling control.

FIGS. 4A-4B illustrate an embodiment of a detector array 400 that can beused as detector array 110 in device 100. Detector array 400 includes asubstrate 402 with an array of sensors S1-S9 formed thereon. In theillustrated embodiment sensors S1-S9 form a regularly shaped 3-by-3array of sensors, but in other embodiments the sensor array can have agreater or lesser number of sensors, and the sensors can be arranged inany pattern, regular or irregular.

A cover 404 is bonded to the perimeter of substrate 402 to form a cavity410 within which sensors S1-S9 are located. Cover 404 also includes aninlet 406 through which fluid can enter from gas chromatograph 108 andan outlet 408 through which fluid can exit to pump 112. A heater 412 isformed on the side of substrate 402 opposite the side where cover 404 isattached to control the temperature of detector array 400, and hence thesensors within the detector array, during operation. Although not shownin the Fig., detector array 400 of course includes outputs by whichsignals generated by sensors S1-S9 can be output for processing.

Each sensor S1-S9 includes a surface with a coating thereon. Eachcoating used will have an affinity for one or more of the particularchemicals being detected, such that the coating absorbs or chemicallyinteracts with its corresponding chemical or chemicals. The interactionbetween coating and chemical in turn changes a physical property of thesensor such as resonant frequency, capacitance or electrical resistance,and that changed physical property of the sensor can be measured using atransducer or other measurement device. The particular coatings chosenfor sensors S1-S9 will depend on the chemicals that sensor array 110will be used to detect. The chemical affinity of coatings also variesstrongly with temperature, so that the operating temperature rangeshould be considered in selecting coatings. In an embodiment wheresensor array 110 will be used to detect volatile organic compounds inhuman breath—such as benzene, toluene, n-octane, ethylbenzene,m,p-xylene, α-pinene, d-limonene, nonanal, and benzaldehyde,2-methylhexane, 4-methyloctane, and so on—coatings that can be used indifferent applications include amorphous copolymers of2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxide (PDD) andtetrafluoroethylene (TFE), PtCl2 (olefin), C8-MPN, etc.

Although the illustrated embodiment has nine sensors, the number ofsensors needed depends on the number of different chemicals to bedetected, and on the nature of the coatings used on the sensors. In anembodiment where each coating absorbs or chemically interacts with onlyone chemical the number of sensors can correspond exactly to the numberof chemicals to be detected, but in other embodiments it can bedesirable to have a given coating on more than one sensor forredundancy. In most cases, however, there is no one-to-one correlationbetween chemicals to coatings; in other words, each coating reacts withmore than one different chemical and the reaction between differentchemicals and a given coating will vary in nature and strength. Adetector array having sensors with different coatings is thereforeuseful because the response of the detector array can have differentpatterns for different gases.

In one embodiment of sensor array 400, sensors S1-S9 are MEMS sensorspositioned on the surface of substrate 402, meaning that they aresurface micromachined sensors. In other embodiments using MEMS sensors,however, sensors S1-S9 can be bulk micromachined sensors, meaning thatat least some of the MEMS sensors are formed within substrate 402instead of on the surface. Still other embodiments of sensor array 110using MEMS sensors can include combinations of surface-micromachined andbulk-micromachined sensors. Different types of MEMS sensors can be used,depending on the application and the required sensitivity. Examples ofMEMS sensors that can be used include chemiresistors, bulk acoustic wave(BAW) sensors, etc. In other embodiments of detector array 400, one ormore of sensors S1-S9 can be a non-MEMS sensor. Examples of non-MEMSsensors that can be used in detector array 400 include quartz crystalmicrobalance (QCM) or surface acoustic wave (SAW) sensors with quartz orgallium arsenide (GaAs) substrates.

During operation of MEMS detector array 400 in device 100, fluid fromgas chromatograph 108 enters through inlet 406 and passes into cavity410. Fluid entering cavity 410 carries time-domain separated chemicals.As each chemical enters cavity 410 it interacts with one or more sensorswhose coating has an affinity for that chemical. The interaction of thechemical with the sensor is sensed and measured, and the presence andconcentration of the particular chemical can be extracted. As more fluidflows into cavity 410, the first chemical is pushed out of cavity 410through outlet 408 and fluid with the next time-domain-separatedchemical enters cavity 410, interacts with the sensor array and ismeasured. This process continues until all the time-domain-separatedchemicals from gas chromatograph 108 have flowed through detector array110. In some embodiments where the affinity of the coatings for theirchemicals is not strong, detector array 110 can be re-usable: after alltime-domain-separated chemicals have been sensed, heater 412 can beactivated to heat the sensors and cause the coatings to release therespective chemicals with which they interacted, making the interactionreversible. In embodiments where the affinity of each coating for itschemicals could be strong, heating of the sensor array could helprelease the partially absorbed gas from the coating materials.

FIG. 4C illustrates an alternative embodiment of the operation ofdetector array 400 in device 100. In this embodiment of operation, bychoosing the chemical sensitivities of individual detectors S1-S9detector array 400 can be used to detect analytes (e.g., chemicals suchas gases or volatile organic compounds (VOCs)) that were eitherunseparated or not completely separated (e.g., partially separated) byGC 108. The top graph illustrates an example of the output of GC 108. Inthis example the fluid flowing through system 100 contains sevenanalytes, but GC 108 could not completely separate all seven: analytes1-3 were completely separated by GC 108, as indicated by their narrowpeaks on the graph, but analytes 4-5 could not be completely separated,nor could analytes 6-7, as indicated by their broad peaks in the graph.In such an example, it can nonetheless be possible to correctly detectanalytes 4-7 by choosing individual detectors S1-S9 in detector array400 to be selective to the analytes that GC 108 cannot separate or, putdifferently, to be unresponsive to analytes that are can be completelyseparated. For example, the second graph in FIG. 4C illustrates theresponse of detector S4 where detector S4 has been chosen to beunresponsive to analytes 5-7, so that detector S4 can detect analyte 4even though it wasn't completely separated by GC 108. Similarly, thethird graph in FIG. 4C illustrates the response of detector S5 wheredetector S5 has been chosen to be unresponsive to analytes 4 and 7, sothat detector S5 can detect analytes 5 and 6 even though they weren'tcompletely separated by GC 108. Finally, the last graph in FIG. 4Cillustrates the response of detector S6 where detector S6 has beenchosen to be unresponsive to analytes 4, 5 and 6, so that detector S6can detect analyte 7 even though it wasn't completely separated by GC108. In this way, GC 108 and detector array effectively cooperate toseparate chemicals that cannot be separated by GC 108 alone.

FIG. 5 illustrates an embodiment of a system 500 using an alternativeembodiment of a MEMS-based gas analysis device 502. Device 502 is inmost respects similar to device 100. The primary difference betweendevice 502 and device 100 is the presence in device 502 of a wirelesstransceiver circuit 504 and an antenna 506 mounted on substrate 102.Wireless transceiver circuit 504 can both transmit (Tx) data and receive(Rx) data and is coupled to reading and analysis circuit 128 and antenna506.

In one embodiment of system 500, transceiver 504 can be used towirelessly transmit raw data from reading and analysis circuit 128 toone or both of a router 508 and a computer 510. When transmitted torouter 508, the data can then be re-transmitted to another destinationfor analysis. For example, in an application where device 502 is usedfor health-related chemical analysis, data sent to router 508 can bere-transmitted to one or more of a doctor's office, a hospital, agovernment health department, or someplace else for analysis andinterpretation. After analysis is complete, or if there is a problemwith the data, the doctor's office, hospital or health department cansend instructions to device 502 through router 508, antenna 506 andtransceiver 504 to signal the result, to try to fix or improve the data,or to signal that the test must be performed again.

Continuing with the same health-care example, in the same or anotherembodiment of system 500, wireless transceiver 504 can be used totransmit raw data to computer 510. Computer 510 can either forward theraw data to a doctor, hospital, etc., as did the router, or can analyzethe data with software installed thereon to provide extract informationfrom the data, such as one or more possible medical diagnoses, andprovide the extracted information to the user of device 502. When itprovides analysis and medical diagnoses, computer 510 can also forwardthe diagnosis, alone or with the analysis and raw data, on to thedoctor, hospital, etc. As with the router, the doctor's office, hospitalor health department can send instructions to device 502 throughcomputer 510, antenna 506 and transceiver 504 to try to fix or improvethe data, to signal that the test must be performed again, and so on.

Again continuing with the same health-care example, in still anotherembodiment of system 500 the raw data can be processed, and informationsuch as potential diagnoses extracted from the data, by reading andanalysis circuit 128. The potential diagnoses determined by reading andanalysis circuit 128 can then be sent to computer 510 to be reviewed bythe user and/or forwarded, or can be immediately forwarded alone or withthe supporting raw data to the doctor's office, etc.

FIG. 6 illustrates an embodiment of a system 600 using an alternativeembodiment of a MEMS-based gas analysis device 602. Device 602 is inmost respects similar to device 502. The primary difference betweendevice 502 and device 602 is that the wireless transceiver circuit 504and antenna 506 are replaced with a hardware data interface 604 coupledto reading and analysis circuit 128. In one embodiment, hardware datainterface 604 could be a network interface card, but in otherembodiments hardware data interface can be an Ethernet card, a simplecable plug, etc. External devices can be connected to device 602 throughtraditional means such as cables. Although it has a differentcommunication interface, device 602 and system 600 have all the samefunctionality as device 502 and system 500. As with system 500, insystem 600 MEMS-based gas analysis device 602 can transmit data to, andreceive data from, one or both of a computer 608 and a wireless device606, such as a cell phone or personal digital assistant (PDA). Whentransmitted to wireless device 606 the data can then be forwarded to adoctor's office, hospital, or government health department, and therecipients of the data can in turn send data or instructions back to gasanalysis device 602 through the wireless device. As in system 500, whendata is transmitted to computer 608 it can be forwarded or can beanalyzed by the computer and the result displayed for the user and/orforwarded, and instructions can be transmitted to device 602 throughcomputer 608. Similarly, the data from gas analysis device 602 can beanalyzed by reading and analysis circuit 128. After analysis by circuit128, the extracted information (e.g., one or more diagnoses) and/or theraw data can be forwarded via the hardware data interface 604.

FIG. 7 illustrates an alternative embodiment of a MEMS-based gasanalysis device 700. Device 700 is in most respects similar to device100. The primary difference between system 700 and device 100 is thatdevice 700 includes an on-board display 702 for conveying to a user theresults of the analysis performed by reading and analysis circuit 128.

The illustrated embodiment uses an on-board text display 702, forexample an LCD screen that can convey text information to a user. Forexample, in a health care example display 702 could be used to displaythe test results in analog numbers indicating the situation of patients.Display 702 could indicate a positive or negative diagnosis, couldindicate probabilities of a given diagnosis, or could indicate the rawdata from the detector array. In another health care embodiment, simplerdisplays can be used, such as one with three lights that indicate apositive, negative, or indeterminate result depending on which light isswitched on.

FIG. 8 illustrates an alternative embodiment of a MEMS-based gasanalysis device 800. Device 800 is in most respects similar to device100. The primary difference between device 800 and device 100 is that indevice 800 one or more elements of fluid handling assembly 101 arereplaceable. In the illustrated embodiment, the elements are madereplaceable by mounting them onto substrate 102 using sockets: filterand valve assembly 104 is mounted to substrate 102 by socket 804,pre-concentrator 106 is mounted to substrate 102 by socket 806, gaschromatograph 108 is mounted to substrate 102 by socket 808, detectorarray 110 is mounted to substrate 102 by socket 810, and pump 112 ismounted to substrate 102 by socket 812. In one embodiment, sockets804-812 are sockets, such as zero insertion force (ZIF) sockets, thatpermit easy replacement by a user, but in other embodiments other typesof sockets can be used. Although the illustrated embodiment shows allthe components of fluid handling assembly 101 being replaceable, inother embodiments only some of the components such as pump 112 anddetector array 110 can be made replaceable.

FIG. 9 illustrates an alternative embodiment of a MEMS-based gasanalysis device 900. Gas analysis device 900 is in most respects similarto device 100. The primary difference between device 900 and device 100is that device 900 includes provisions for an external pre-concentrator902 (i.e., a pre-concentrator not mounted on substrate 102). In theembodiment shown, a valve 904 is placed between pre-concentrator 106 andgas chromatograph 108, and provisions are made to attach externalpre-concentrator 902 to the valve. Valve 904 allows the user to useexternal pre-concentrator 902 instead of, or in addition to, on-boardpre-concentrator 106. In one embodiment external pre-concentrator 902 isa breath collection bag, but in other embodiments it can be somethingdifferent. In an alternative embodiment of device 900 (not shown),pre-concentrator 106 can be permanently removed and replaced by externalpre-concentrator 902. In another embodiment where externalpre-concentrator 902 replaces pre-concentrator 106, instead of insertinga valve between pre-concentrator 106 and gas chromatograph 108, externalpre-concentrator 902 can be coupled upstream of the filter and valveassembly 104.

FIG. 9A illustrates a further alternative embodiment of a gas analysisdevice 950. Gas analysis device 950 is in most respects similar todevice 100. The primary difference between device 950 and device 100 isthat device 950 includes a three-way valve TV1 in the fluid connectionbetween pre-concentrator 106 and gas chromatograph (GC) 108, as well asa fluid connection 952 that couples three-way valve TV1 to the fluidconnection between detector array (DA) 110 and pump 112. Three-way valveTV1 and fluid connection 952 provide device 950 with different fluidpaths for different operation modes.

When device 950 is operated in sampling mode (e.g., collecting a breathsample for analysis), three-way valve TV1 is set so that the fluid flowsthrough device 950 along the flow path shown with the dotted linelabeled S. In sampling mode, fluid enters device 950 and passes throughfilter/valve 104 and through pre-concentrator 106. Following thepre-concentrator, three-way valve TV1 diverts the flow into fluidconnection 952 so that the flow bypasses GC 108 and DA 110 and goes intothe inlet of pump 112, which then exhausts the fluid to the atmosphere.When device 950 is operated in analysis mode (e.g., when separatinganalytes such as VOCs), three-way valve TV1 is set so that the fluidflows through device 950 along the flow path shown with the dotted linelabeled A. In analysis mode, fluid enters device 950 and passes throughfilter/valve 104 and through pre-concentrator 106. Following thepre-concentrator, three-way valve TV1 is set to direct the flow into GC108 instead of fluid connection 952. After passing through GC 108, theflow continues into DA 110 for analysis and then goes into pump 112,after which it is exhausted to the atmosphere.

FIG. 9B illustrates a further alternative embodiment of a gas analysisdevice 975. Gas analysis device 975 is in most respects similar todevice 100. The primary difference between device 975 and device 100 isthat device 975 includes additional elements to provide different fluidpaths for different operation modes. Device 975 includes a firstthree-way valve TV2 in the fluid connection between filter/valve unit104 and pre-concentrator 106, as well as a second three-way valve TV3 inthe fluid connection between PC 106 and gas chromatograph (GC) 108. Afluid connection 977 couples second three-way valve TV3 to a thirdthree-way valve TV4, which is in turn coupled to the inlet of pump 112by fluid connection 979. Similarly, a fluid connection 983 couples firstthree-way valve TV2 to a fourth three-way valve TV5, and fourththree-way valve TV5 is in turn coupled to the outlet of pump 112 byfluid connection 981.

When device 975 is operated in sampling mode (e.g., collecting a breathsample for analysis), three-way valves TV2-TV5 are set so that the fluidflows through device 975 along the flow path shown with the dotted linelabeled S. In sampling mode, fluid enters device 975 and passes throughfilter/valve 104 and pre-concentrator 106. Following pre-concentrator106, three-way valve TV3 diverts the flow into fluid connection 977, sothat the flow by-passes GC 108 and DA 110 and goes to three-way valveTV4. Three-way valve TV4 is set so that it directs the flow to the inletof pump 112, which then exhausts the fluid into fluid connection 981.Fluid connection 981 directs the fluid from pump 112 to three-way valveTV5, which is set to exhaust the fluid to the atmosphere. When device975 is operated in analysis mode (e.g., when separating analytes such asVOCs), three-way valves TV2-TV5 are set so that the fluid flows throughdevice 975 along the flow path shown with the dotted line labeled A. Inanalysis mode, pump 112 draws fluid from the atmosphere into device 975through three-way valve TV4 and fluid connection 979. Fluid connection981 is coupled to the outlet of pump 112 and carries the fluid tothree-way valve TV5, which is set to direct the fluid into fluidconnection 983. Fluid connection 983 then carries the fluid to three-wayvalve TV2, which is set to direct the fluid to the inlet of PC 106.Three-way valve TV3 is set so that fluid exiting PC 106 is directed intoGC 108, then into DA 110, and then into the atmosphere.

FIG. 10 illustrates an embodiment of a cascaded gas chromatograph (CGC)1000 using analyte focusing. CGC 1000 includes a first gas chromatograph(GC) 1002 having a fluid inlet 1006 and a fluid outlet 1008. A second GC1004 has a fluid inlet 1010 and a fluid outlet 1012, with the fluidinlet 1010 coupled to the fluid outlet 1008 by a fluid connection.Surrounding the fluid connection between GC 1002 and GC 1004 are acooling section 1016 and a heating section 1018. The entire assembly ispositioned within a GC oven 1014.

In operation of CGC 1000, a carrier gas including one or more chemicals(also known as an analytes) enters first GC 1002 through its fluid inlet1006. After the analytes circulates through GC 1002, they exit the GCthrough fluid outlet 1008 and flow in the fluid connection throughcooling section 1016, where a cold air jet is directed into the coolingsection to cool the analytes. The cold air used in cooling section 1016can be produced using either liquid nitrogen or dry ice. After flowingin the fluid connection through cooling section 1016, the analytescontinue into heating section 1018. In heating section 1018, a hot airjet is used to heat the previously cooled analytes. Following heatingsection 1018, the analytes proceed through fluid inlet 1010 to enter GC1004 for further separation. CGC 1000 is bulky and expensive, andtherefore cannot be used as portable gas analysis systems. Moreover,only a small section of CGC 1000 can be cooled due to its large thermalmass.

FIGS. 11A-11B illustrate an embodiment of focusing analytes (such asvolatile organic compounds (VOCs)by cooling and/or heating a GC. In eachfigure, the lower graph illustrates a temperature profile (e.g., avariation of temperature with time) that is applied to a GC, while theupper graph illustrates the response of a detector coupled to that GC.FIG. 11A illustrates an approach in which the GC begins at an initialtemperature that is then ramped up to a target temperature at a desiredramping rate. With this temperature profile, gases 1, 2 and 3, areseparated, but other gases remain unseparated by the GC. In mostsituations, the input analytes/VOCs have a broad concentrationdistribution when entering the GC column. The spectrum becomes wider andlower as analytes are traveling within the GC column while separatingfrom each other in time at output of GC. In most situations, some of theanalyte spectrums are too wide and overlap with each other, whichresults in non-separated gases as show in the figure.

FIG. 11B illustrates an alternative approach. The temperature profile isshown in the bottom graph: the temperature of the chromatograph beginsat initial temperature and is then cooled (reduced or lowered) to alower temperature. After reaching the lowest temperature desired, thecooling is followed by heating the chromatograph to an operatingtemperature. The results of applying the temperature profile shown inthe lower graph are shown in the detector response graph. The same gases1-3 are separated from the analyte, but because of the focusing effectof cooling the analyte, gases that were previously unseparated are nowseparated, as shown by the sharp peaks in the detector response. Thecooling produces an immediate focusing effect and narrowing (sharpening)of the spectrum profile. The micro-GC is then heated to targetedtemperature with the desired ramping rate to achieve analyte/VOCseparation. Due to the operation of micro-GC cooling, the outputspectrums are sharper compared to non-cooling operation. With sharperspectrums, gases/VOCs overlap at the micro-GC output will be reduced. Asa result, more analytes can be resolved with micro-GC cooling.

FIG. 11C illustrates an embodiment of a temperature profile that can beapplied to a GC to obtain analyte focusing. For purposes of thisapplication, the term “temperature profile” refers to a variation oftemperature with time. In FIG. 11C, the vertical axis represents atemperature of the GC, while the horizontal axis represents time.

Prior to time t₀, the GC is maintained at an initial temperature T0. Inone embodiment, initial temperature T0 is substantially room temperature(typically around 20° C., but not limited to this temperature), but inother embodiments the initial temperature can be a temperature lower orhigher than room temperature. Starting at time t₀, the profile begins afirst time period from time t₀ until time t₁ during which thetemperature of the GC is lowered (i.e., the GC is cooled) until itreaches a temperature T1 lower than the initial temperature T0. In oneembodiment temperature T1 is a temperature below freezing, for example−10° C., but in other embodiments T1 can be any temperature lower thaninitial temperature T0. In one embodiment the duration of the firstperiod (t₁-t₀) can be from 2-10 seconds, but in other embodiments thefirst period can be shorter or longer. Moreover, although theillustrated embodiment shows the temperature decreasing linearly in thefirst period, in other embodiments the temperature decrease in the firstperiod need not be linear.

At the end of the first period, after reaching temperature T1 at timet₁, the temperature profile enters a second period from time t₁ to timet₂ during which the temperature of the GC is held substantially at orabout T1. In one embodiment the duration of the second period (t₂-t₁)can last from a few seconds to a couple of minutes, but in otherembodiments the duration of the second period can be essentially zero,such that t₂=t₂. At the end of the second period at time t₂, thetemperature profile enters a third period from time t₂ to time t₃ duringwhich the GC temperature is increased from T1 to a target temperatureT2. In one embodiment T2 can be about +80° C., but in other embodimentsother target temperatures are possible. In one embodiment the durationof the third period (t₃-t₂) can be from 2-10 seconds, but in otherembodiments the third period can be shorter or longer. Moreover, theillustrated embodiment shows the temperature increasing linearly at thebeginning of the third period and then increasing more slowly andnon-linearly until the temperature reaches T2, but in other embodimentsother distributions of temperature with time are possible. For example,in one embodiment the temperature increase during the third period canbe completely linear from t₂ to t₃. In another example, the temperatureof the gas chromatograph can initially overshoot temperature T2 and thenbe cooled to return the temperature to T2.

FIGS. 12A-12C illustrate the construction and operation of an embodimentof a system 1200. System 1200 includes a GC 1202 having a fluid inlet1204 and a fluid outlet 1206. A detector 1208 is coupled to the fluidoutlet 1206 by a fluid connection. GC 1202 includes a temperaturecontrol that allows the GC to be heated, cooled, or both heated andcooled, for example by using a temperature profile such as the oneillustrated in FIG. 11C. In one embodiment, GC 1202 can have theconstruction illustrated in FIG. 3B-3C, but in other embodiments it canhave a different construction, such as the one shown in FIGS. 3D-3E orsome other construction altogether. Detector 1208 can be any kind ofchemical detector; in one embodiment, it can be a detector array such asdetector array 400 shown in FIGS. 4A-4B, but in other embodiments otherkinds of detector arrays can be used. Although not shown in the figure,the temperature control of gas chromatograph 1202 can be coupled to acontrol circuit (such as control circuit 126 when chromatograph 1202 isused in gas analysis systems such as the ones shown in FIGS. 1A-1B and5-9) that applies the temperature profile to the temperature control.

FIGS. 12B-12C illustrates the results obtained with system 1200 whentemperature profiles such as the one shown in FIGS. 11A-11C are appliedto GC 1200 and when a flame ionization detector (FID) is used (FIG. 12B)or when an acoustic resonator detector such as a surface acoustic wave(SAW) or QCM detector (FIG. 12C). Both figures show the results ofapplying three temperature profiles to GC 1202: a first temperatureprofile in which the temperature is kept at a constant 50 C, a secondtemperature profile in which the temperature is reduced to 10° C., heldfor 15 seconds, and then increased to 50 C, and a third temperatureprofile in which the temperature is reduced to −15 C, held for 15seconds, and then increased to 50 C. The results obtained from bothdetectors show significant improvement in VOC (analyte) spectrumsharpening (narrower and higher peaks). The lower the coolingtemperature that is applied, the better the sharpening of the spectrum.With an increase on the spectrum height, the detector's detection limitcan be improved. Meanwhile, with a narrower VOC spectrum, additionalVOCs can be resolved (separated) from neighboring VOCs.

FIGS. 13A-13C illustrate the construction and operation of a cascadedgas chromatograph (CGC) 1300. Embodiments of CGC 1300 can be used inplace of, or one or more of its components can be used to supplement,gas chromatograph (GC) 108 and detector 110 in gas analysis systems suchas the ones shown in FIGS. 1A-1B and 5-9. CGC 1300 includes a first gaschromatograph (GC) 1302 coupled to a second GC 1304. In the illustratedembodiment, GCs 1302 and 1304 are coupled in series such that outlet1308 of GC 1302 is coupled to inlet 1310 of GC 1304 by a fluidconnection 1314. Outlet 1312 of GC 1304 is coupled to a detector 1318 bya fluid connection 1316, although in other embodiments outlet 1312 couldbe coupled to some entirely different component. Although theillustrated embodiment has only two GCs, in other embodiments one ormore additional GCs, as well as other components such as additionalfluid connections, flow splitters, three-way valves detectors and switchvalves, can be added to form a larger cascade of GCs.

In the illustrated embodiment, GCs 1302 and 1304 are MEMS GCs withindividual temperature controls, such as those shown in FIG. 3B or 3C,but in other embodiments they can be the capillary column GCs shown inFIGS. 3D-3E or some other construction altogether. The individualtemperature controls allow the operating temperature of each GC to becontrolled independently of the other. In other embodiments GCs 1302 and1304 need not be of the same type—that is, CGC 1300 can include bothMEMS and non-MEMS chromatographs. In some embodiments bothchromatographs can have the same kind of temperature control, but inother embodiments both chromatographs need not have the same temperaturecontrol; for example, in the illustrated embodiment with two MEMSchromatographs, GC 1302 can have an integrated temperature control asshown in FIG. 3B, while GC 1304 has an external temperature control, asshown in FIGS. 3C-3E. In one embodiment, detector 1318 is a detectorarray as shown in FIGS. 4A-4B, but in other embodiments it can be adifferent type of detector. Although not shown in the figure, thetemperature control of GCs 1302 and 1304 can be coupled to a controlcircuit (such as control circuit 126 when CGC 1300 is used in gasanalysis systems such as the ones shown in FIGS. 1A-1B and 5-9) thatapplies a temperature profile to the temperature control. Because thetemperature controls of GCs 1302 and 1304 are independent, in someembodiments different temperature profiles can be applied to each GC.

In some embodiments, GCs 1302 and 1304 can have the samecharacteristics, but in other embodiments GCs 1302 and 1304 need nothave the same characteristics and can have different column lengths,column coatings, operating temperatures, etc. In one embodiment, forexample, GC 1302 can be coated with material A, which can be especiallyselective to polar or non-polar chemicals, and can have its optimumtemperature control profile to separate specific chemicals. Meanwhile,GC 1304 can have a different column length and can be coated withanother material B, which can separate different chemicals that GC 1302cannot resolve (separate); in other words, GC 1304 is complementary toGC 1302. Since each GC in the configuration can has its own temperaturecontrol, GC 1304 can be optimized to separate the remaining gases ofinterest that are not resolved (separated) by GC 1302. The separatedgases can then be detected by detector 1318 at output of GC 1304.

In operation of CGC 1300, a carrier fluid having one or more chemicalstherein enters GC 1302 through inlet 1306 and flows through the GC'scolumn while a temperature profile from FIGS. 11C or 13B is applied tothe GC's temperature control. The carrier fluid, with any chemicals notresolved (separated) by GC 1302, exits through outlet 1308 into fluidconnection 1314. Fluid connection 1314 carries the fluid into GC 1304,where the fluid flows through the GC's column while a temperatureprofile from FIGS. 11C or 13C, which can be the same or different thanthe profile applied to GC 1302, is applied to the temperature control ofGC 1304. As a result, some or all of the unresolved chemicals remainingafter GC 1302 are separated. Outlet 1312 of GC 1304 is coupled to adetector 1318, which can then be used to detect the chemicals separatedfrom the carrier fluid by the two GCs.

FIGS. 14A-14B together illustrate the construction and operation of anembodiment of a multi-dimensional gas chromatograph 1400. Embodiments ofgas chromatograph 1400 can be used in place of, or one or more of itscomponents can be used to supplement, gas chromatograph (GC) 108 and/ordetector 110 in gas analysis systems such as the ones shown in FIGS.1A-1B and 5-9.

Multi-dimensional gas chromatograph 1400 includes a first gaschromatograph (GC) 1402, a second GC 1408 and a third GC 1414 fluidlycoupled to each other by several components that together form a “Deanswitch.” Each of the first, second and third GCs has its own temperaturecontrol that is independent of the others. In one embodiment, the first,second and third GCs can have the construction illustrated in FIGS.3A-3C, but in other embodiments they can have a different construction,such as the one shown in FIGS. 3D-3E or some other constructionaltogether. In still other embodiments the first, second and third gaschromatographs need not have the same construction. As in CGC 1300, insome embodiments GCs 1402, 1408 and 1414 can have the samecharacteristics, but in other embodiments the individual GCs need nothave the same characteristics and can have different column lengths,column coatings, operating temperatures, etc. Although not shown in thefigure, the temperature controls of GCs 1402, 1408 and 1414 can becoupled to a controller or control circuit (such as control circuit 126when multi-dimensional chromatograph 1400 is used in gas analysissystems such as the ones shown in FIGS. 1A-1B and 5-9) that appliestemperature profiles to the temperature controls of the individual GCsduring operation.

First GC 1402 includes a fluid inlet 1404 through which the analytes(e.g., volatile organic compounds (VOCs)) enter the GC and a fluidoutlet 1406 through which separated chemicals exit GC 1402. Fluid outlet1406 is coupled by fluid connection 1420 to a first Y-splitter Y1. FirstY splitter Y1 is coupled to second Y-splitter Y2 by fluid connection1422 and to third Y-splitter Y3 by fluid connection 1426. SecondY-splitter Y2 is further fluidly coupled to fluid inlet 1410 of secondGC 1408 by fluid connection 1424, and fluid outlet 1412 of GC 1408 iscoupled to a detector 1446. Similarly, third Y-splitter Y3 is coupled tofluid inlet 1416 of GC 1414 by fluid connection 1428, and fluid outlet1418 of GC 1414 is coupled to a detector 1448.

Second Y-splitter Y2 is coupled by secondary fluid connection 1430 toflow rate restrictor 1432, and flow-rate restrictor 1432 is coupled byfluid connection 1434 to a three-way valve 1436. Similarly, thirdY-splitter Y3 is coupled by secondary fluid connection 1442 to flow raterestrictor 1440, and flow-rate restrictor 1440 is coupled by fluidconnection 1438 to three-way valve 1436. Three-way valve 1436 is alsocoupled to a source of a secondary carrier gas. A flow resistor 1444 canoptionally be fluidly coupled between fluid connections 1430 and 1442.The group of elements including the Y-splitters, the flow raterestrictors, the flow resistor, and the fluid connections among themtogether form a “Dean switch.” Use of the Dean switch permits the use of“heart-cutting.” In the heart-cutting technique, one or more unresolved(i.e., unseparated) analytes from a first chromatograph (firstdimension) are transferred to one or more additional chromatographshaving a different polarity (second dimension) where the separation ofthe compounds un-separated by the first chromatograph will be achieved.

In operation of multi-dimensional gas chromatograph 1400, the carriergas containing chemicals (analytes) is directed into fluid inlet 1404 ofGC 1404. Separated and unseparated analytes exit through fluidconnection 1420 to Y-splitter Y1. At the same time, three-way valve 1436is set to direct a secondary carrier gas into fluid connection 1438, sothat the secondary carrier gas will flow through flow rate restrictor1440 to Y-splitter Y3, where a portion of the secondary gas will flowinto third GC 1414 and the remaining portion will flow throughY-splitters Y1 and Y2 into second GC 1408. When flow resistor 1444 ispresent, part of the secondary gas flows though the flow resistor. Thepath taken by the secondary carrier gas is illustrated by the dottedline labeled S. As a result of the flow of secondary carrier gas, theprimary flow path, which carries analytes exiting from first GC 1402, isdirected into second GC 1408, as shown by the dotted line labeled P.FIG. 14B illustrates another mode of operation of multi-dimensional GC1400 in which flow is directed into third GC 1414 instead of second GC1408 by switching three-way valve 1436 to its other position, such thatthe flow path S of the secondary carrier gas now changes the primarypath P. During operation, temperature profiles are applied to theindividual GCs to improve separation of the analytes. Because thetemperature controls of GCs are independent, in some embodimentsdifferent temperature profiles can be applied to each GC.

FIG. 15 illustrates an alternative embodiment of a multi-dimensional gaschromatograph 1500. Embodiments of gas chromatograph 1500 can be used inplace of, or one or more of its components can be used to supplement,gas chromatograph (GC) 108 and/or detector 110 in gas analysis systemssuch as the ones shown in FIGS. 1A-1B and 5-9. Multi-dimensionalchromatograph 1500 is in most respects similar to multi-dimensionalchromatograph 1400. The primary difference between chromatographs 1400and 1500 is that in chromatograph 1500 elements of the Dean switch areformed on a microchip 1502. In the illustrated embodiment, Y-splittersY1, Y2 and Y3 are formed on chip 1502 along with flow rate restrictors1432 and 1440 and fluid connections between these elements. In otherembodiments, additional elements such as flow resistor 1444 can also beformed on chip 1502.

FIG. 16 illustrates another alternative embodiment of amulti-dimensional gas chromatograph 1600. Embodiments of gaschromatograph 1600 can be used in place of, or one or more of itscomponents can be used to supplement, gas chromatograph (GC) 108 and/ordetector 110 in gas analysis systems such as the ones shown in FIGS.1A-1B and 5-9. Multi-dimensional chromatograph 1600 is in most respectssimilar to multi-dimensional chromatographs 1400 and 1500. Theindividual GCs 1602, 1604 and 1606 in chromatograph 1600 have at leastthe same features and characteristics as the individual GCs inchromatographs 1400 and 1500. The primary difference betweenchromatograph 1600 and chromatographs 1400 and 1500 is that inchromatograph 1600 certain elements of the Dean switch are integrallyformed in the individual GCs. In the illustrated embodiment, Y-splittersY1 is integrally formed in first GC 1602, along with fluid connectionsthat allow GC 1602 to be coupled to the other GCs. Similarly, second GC1604 has flow rate restrictor 1432 and Y-splitter Y2 formed therein,while third GC 1606 has third Y-splitter Y3 and flow rate restrictor1440 formed therein.

Embodiments are disclosed of a new method of gas analyte (e.g.,chemicals such as volatile organic compounds (VOCs)) spectrum sharpeningand separation enhancement using multi-dimensional miniaturized gaschromatography column (GC) or micro-GC configuration. Unlike thetraditional bulky GC system with slow and limited temperature controlflexibility, the disclosed embodiments utilizes miniaturized GC/micro-GCcolumns, which can be cascaded with different coating materials for gasseparation analysis. The micro-GCs are small in size (can be fabricatedinto micro-chip size if necessary) and thus can be promptly cooled downto sub-zero temperature with a simple small cooling device (e.g.,thermoelectric cooler, TE cooler), which cannot be achieved usingtraditional bulky GC unless liquid nitrogen is used. With simple, fast,and direct micro-GC cooling, one can achieve direct column focusingeffect, which sharpens the analyte spectrum and improves the columnseparation power. Furthermore, the disclosed embodiments can alsoinclude a cascade of multiple micro-GCs to form a heart-cutting gaschromatography configuration.

The disclosed embodiments are the first implementation of a direct fastGC cooling on micro-GC with simple cooling device, which allows thepossibility of achieving spectrum sharpening without using liquidnitrogen. Meanwhile, they also improve the detection limit. As a result,the disclosed embodiments can be implemented as a portable gas analysissystem and significantly improve the system resolution and detectionlimit.

The above description of illustrated embodiments of the invention,including what is described in the abstract, is not intended to beexhaustive or to limit the invention to the precise forms disclosed.While specific embodiments of, and examples for, the invention aredescribed herein for illustrative purposes, various equivalentmodifications are possible within the scope of the invention, as thoseskilled in the relevant art will recognize. These modifications can bemade to the invention in light of the above detailed description.

The terms used in the following claims should not be construed to limitthe invention to the specific embodiments disclosed in the specificationand the claims. Rather, the scope of the invention is to be determinedentirely by the following claims, which are to be construed inaccordance with established doctrines of claim interpretation.

1. An apparatus comprising: a first gas chromatograph including a fluid inlet, a fluid outlet, and a first temperature control; and a controller coupled to the first temperature control, wherein the controller includes logic to apply a first temperature profile to the first temperature control to heat, cool, or both heat and cool the first gas chromatograph.
 2. The apparatus of claim 1 wherein the first temperature profile comprises: a first time period during which the temperature control cools the gas chromatograph from an initial temperature to a first temperature; and a second time period during which the temperature control heats the gas chromatograph from the first temperature to a second temperature.
 3. The apparatus of claim 2 wherein the first temperature profile further comprises a third time period during which the temperature control holds the gas chromatograph at the first temperature.
 4. The apparatus of claim 2 wherein the initial temperature is substantially room temperature, the first temperature is lower than room temperature, and the second temperature is greater than room temperature.
 5. The apparatus of claim 2 wherein the temperature change in the first time period and the temperature change in the second time period are both linear.
 6. The apparatus of claim 2 wherein at least one of the temperature change in the first time period and the temperature change in the second time period is non-linear.
 7. The apparatus of claim 1, further comprising: a second gas chromatograph having a fluid inlet, a fluid outlet, and a second temperature control, the fluid inlet of the second gas chromatograph being coupled by a fluid connection to the fluid outlet of the first gas chromatograph and the second temperature control being coupled to the controller, wherein the controller includes logic to apply a second temperature profile to the second temperature control to heat, cool, or both heat and cool the second gas chromatograph.
 8. The apparatus of claim 7 wherein the second temperature profile applied to the second temperature control is different than the first temperature profile.
 9. The apparatus of claim 1, further comprising: a second gas chromatograph having a fluid inlet, a fluid outlet, and a second temperature control; a third gas chromatograph having a fluid inlet, a fluid outlet, and a third temperature control; wherein the fluid outlet of the first gas chromatograph is coupled to the fluid inlets of the second and third gas chromatographs by a heart-cutting valve, wherein the second and third temperature controls are coupled to the controller, and wherein the controller includes logic to apply a second temperature profile to the second temperature control and a third temperature profile to the third temperature control to heat, cool, or both heat and cool the second and third gas chromatographs.
 10. The apparatus of claim 9 wherein the heart-cutting valve comprises: a first Y-splitter coupled to the fluid outlet of the first gas chromatograph; a second Y-splitter coupled to the first Y-splitter, the fluid inlet of the second gas chromatograph, and a first secondary fluid connection; and a third Y-splitter coupled to the first Y-splitter, the fluid inlet of the third gas chromatograph, and a second secondary fluid connection.
 11. The apparatus of claim 10, further comprising a three-way valve coupled to the first secondary fluid connection, the second secondary fluid connection, and a source of a secondary carrier fluid.
 12. The apparatus of claim 10, further comprising a first flow restrictor in the first secondary fluid connection and a second flow restrictor in the second secondary fluid connection.
 13. The apparatus of claim 10 wherein the heart-cutting valve further comprises a flow resistor coupled to the first secondary fluid connection between the first flow restrictor and the second Y-splitter and coupled to the second secondary fluid connection between the second flow restrictor and the third Y-splitter.
 14. The apparatus of claim 10 wherein the heart-cutting valve is formed on a microchip.
 15. The apparatus of claim 11 wherein the first Y-splitter is formed in the first gas chromatograph, the second Y-splitter and the first flow restrictor are formed in the second gas chromatograph, and the third Y-splitter and the second flow restrictor are formed in the third gas chromatograph.
 16. A gas analysis system comprising: a substrate; a gas chromatograph having a fluid inlet and one or more fluid outlets and being mounted to the substrate, the gas chromatograph comprising a first gas chromatograph having a first temperature control; one or more detector arrays having a fluid inlet and a fluid outlet and being mounted to the substrate, wherein the fluid inlet of each of the one or more detector arrays is fluidly coupled to a corresponding one of the one or more fluid outlets of the cascaded gas chromatograph; a control circuit coupled to the cascaded gas chromatograph and to the detector array, wherein the control circuit includes logic to apply a first temperature profile to the first temperature control to heat, cool, or both heat and cool the first gas chromatograph, and wherein the control circuit can communicate with the gas chromatograph and with the one or more detector arrays; and a readout circuit coupled to the one or more detector arrays and to the control circuit, wherein the readout circuit can communicate with the control circuit and the one or more detector arrays.
 17. The gas analysis system of claim 16 wherein the first temperature profile comprises: a first time period during which the temperature control cools the gas chromatograph from an initial temperature to a first temperature; and a second time period during which the temperature control heats the gas chromatograph from the first temperature to a second temperature.
 18. The gas analysis system of claim 17 wherein the first temperature profile further comprises a third time period during which the temperature control holds the gas chromatograph at the first temperature.
 19. The gas analysis system of claim 17 wherein the initial temperature is substantially room temperature, the first temperature is lower than room temperature, and the second temperature is greater than room temperature.
 20. The gas analysis system of claim 16, wherein the gas chromatograph further comprises: a second gas chromatograph having a fluid inlet, a fluid outlet, and a second temperature control, the fluid inlet of the second gas chromatograph being coupled by a fluid connection to the fluid outlet of the first gas chromatograph and the second temperature control being coupled to the controller, wherein the controller includes logic to apply a second temperature profile to the second temperature control to heat, cool, or both heat and cool the second gas chromatograph.
 21. The gas analysis system of claim 20 wherein the first temperature profile is different than the second temperature profile.
 22. The gas analysis system of claim 16, wherein the gas chromatograph further comprises: a second gas chromatograph having a fluid inlet, a fluid outlet, and a second temperature control; a third gas chromatograph having a fluid inlet, a fluid outlet, and a third temperature control; wherein the fluid outlet of the first gas chromatograph is coupled to the fluid inlets of the second and third gas chromatographs by a heart-cutting valve, wherein the second and third temperature controls are coupled to the controller, and wherein the controller includes logic to apply a second temperature profile to the second temperature control and a third temperature profile to the third temperature control to heat, cool, or both heat and cool the second and third gas chromatographs.
 23. The gas analysis system of claim 22 wherein the heart-cutting valve comprises: a first Y-splitter coupled to the fluid outlet of the first gas chromatograph; a second Y-splitter coupled to the first Y-splitter, the fluid inlet of the second gas chromatograph, and a first secondary fluid connection; and a third Y-splitter coupled to the first Y-splitter, the fluid inlet of the third gas chromatograph, and a second secondary fluid connection.
 24. The gas analysis system of claim 16, further comprising a three-way valve coupled to the first secondary fluid connection, the second secondary fluid connection, and a source of a secondary carrier fluid.
 25. The gas analysis system of claim 16, further comprising a pre-concentrator having a fluid inlet and a fluid outlet, wherein the pre-concentrator is mounted on the substrate and coupled to the control circuit, and wherein the fluid outlet of the pre-concentrator is coupled to the fluid inlet of the cascaded gas chromatograph.
 26. The gas analysis system of claim 25, further comprising a filter and valve unit having a fluid inlet and a fluid outlet, wherein the filter and valve unit is mounted to the substrate and coupled to the control circuit, and wherein the fluid outlet of the filter and valve unit is coupled to the fluid inlet of the pre-concentrator.
 27. The gas analysis system of claim 26, further comprising one or more pumps having a fluid inlet and a fluid outlet, wherein each pump is mounted on the substrate and coupled to the control circuit, and wherein the fluid inlet of each pump is coupled to the fluid outlet of a corresponding detector array.
 28. The gas analysis system of claim 27, further comprising: a three-way valve coupled in the fluid connection between the pre-concentrator and the gas chromatograph; and a fluid connection coupled to the three-way valve and to the fluid connections between the one more detector arrays and the corresponding pump.
 29. The gas analysis system of claim 27, further comprising: a first three-way valve coupled in the fluid connection between the filter and the pre-concentrator; a second three-way valve coupled in the fluid connection between the pre-concentrator and the gas chromatograph; a fluid connection coupled to the first three-way valve and to the fluid outlets of the one or more pumps; and a fluid connection coupled to the second three-way valve and to the fluid inlets of the one or more pumps.
 30. The gas analysis system of claim 29, further comprising: a third three-way valve in the fluid connection between the second three-way valve and the inlets of the one or more pumps; and a fourth three-way valve in the fluid connection between the first three-way valve and the outlets of the one or more pumps.
 31. The gas analysis system of claim 16 wherein the readout circuit includes thereon an analysis circuit and associated logic to analyze an output signals received from the one or more detector arrays.
 32. The gas analysis system of claim 31, further comprising an indicator coupled to an output of the analysis circuit to indicate to a user a result of the analysis.
 33. The gas analysis system of claim 16, further comprising a communication interface coupled to the readout circuit to allow the gas analysis system to communicate with an external device.
 34. The gas analysis system of claim 16 wherein one or more detectors in each detector array is selective to a chemical that was unseparated or partially separated by the one or more gas chromatographs.
 35. A process for time-domain separating one or more chemicals from a fluid, the process comprising: injecting a fluid including a plurality of chemicals into a gas chromatograph comprising a first gas chromatograph having a first temperature control; applying a first temperature profile to the first temperature control to heat, cool, or both heat and cool the first gas chromatograph; detecting each of the plurality of time-domain-separated chemicals using one or more sensors in one or more detector arrays coupled to the gas chromatograph; and processing signals from each sensor in the one or more detector arrays to determine the presence and concentration of each chemical.
 36. The process of claim 35 wherein the first temperature profile comprises: a first time period during which the temperature control cools the gas chromatograph from an initial temperature to a first temperature; and a second time period during which the temperature control heats the gas chromatograph from the first temperature to a second temperature.
 37. The process of claim 36 wherein the first temperature profile further comprises a third time period during which the temperature control holds the gas chromatograph at the first temperature.
 38. The process of claim 36 wherein the initial temperature is substantially room temperature, the first temperature is lower than room temperature, and the second temperature is greater than room temperature.
 39. The process of claim 35, further comprising: injecting fluid from the fluid outlet of the first gas chromatograph into a fluid inlet of a second gas chromatograph having a second temperature control; applying a second temperature profile to the second temperature control to heat, cool, or both heat and cool the second gas chromatograph.
 40. The process of claim 35, further comprising: injecting fluid from the fluid outlet of the first gas chromatograph into a fluid inlet of a second gas chromatograph having a second temperature control; injecting fluid from the fluid outlet of the first gas chromatograph into a fluid inlet of a third gas chromatograph having a third temperature control; applying a second temperature profile to the second temperature control to heat, cool, or both heat and cool the second gas chromatograph; and applying a third temperature profile to the third temperature control to heat, cool, or both heat and cool the third gas chromatograph.
 41. The process of claim 35, further comprising pre-concentrating the plurality of chemicals in a pre-concentrator before time-domain separation.
 42. The process of claim 41, further comprising filtering the fluid prior to pre-concentrating the chemicals.
 43. The process of claim 35 wherein processing the signals further comprises analyzing the presence and concentration of each chemical to determine a meaning.
 44. The process of claim 35 wherein detecting each of the plurality of time-domain-separated chemicals further comprises detecting one or more unseparated or partially separated chemicals using a sensor selective to the unseparated or partially separated chemicals. 